1. Technical Field of the Invention
This invention relates to a rotary connector for making electrical connection between a rotary member and a fixed member, for example, in a steering device of an automobile in which the number of revolutions of the rotary member is finite.
2. Related Art
In a rotary connector 1 of the type described, a cylindrical rotator (rotary member) 5 is rotatably mounted in an inner receiving portion 3a of a cylindrical undercover (fixed member) 3 in concentric relation thereto, as shown in FIG. 4. A flexible flat cable 7 is received in a spirally-wound manner between the inner receiving portion 3a and the rotator 5. A carrier 11 is provided between the rotator 5 and the flexible flat cable 7, and has a plurality of idlers 9 for absorbing slack of the flexible flat cable 7 so as to smoothly effect the winding-up and feeding of the flexible flat cable 7.
A cylindrical cover (fixed member) 13 is fitted on the undercover 3. The cover 13 has a concentric hole 13a, and an upper portion of the rotator 5 projects from the cover 13 through the hole 13a. An annular upper cover (rotary member) 15 is provided on an upper surface of the cover 13, and this upper cover 15 is fixed to the rotator 5 so as to rotate therewith. A vehicle body-side connector 17 is mounted at an outer periphery-side end of the flexible flat cable 7, and this vehicle body-side connector 17 is fixed to the undercover 3. Steering-side connectors 19 are mounted at a center-side end of the flexible flat cable 7, and the steering-side connectors 19 are passed through the hole 13a in the cover 13, and are fixed to the upper cover 15.
In the rotary connector 1 of this construction, the undercover 3 is fixed to a steering column, and the rotator 5 is fixed to a steering shaft through the upper cover 15 which is rotated by engaging an engagement boss 16 with an engagement hole in the steering (not shown). With this construction, slack of the flexible flat cable 7f due to the rotation of a handle is absorbed by the winding-up and feeding of the flexible flat cable 7, and thereby enabling auxiliary equipments (the rotary side) (such as a horn switch, a steering switch, control switches of an audio and so on, and an inflator) to be electrically connected to a wire harness (the fixed side) installed on a vehicle body.
However, in the above related rotary connector, when the undercover 3 and the rotator 5 are rotated relative to each other, a turned portion 7a of the flexible flat cable 7, shown in FIG. 7, moves in the annular space formed by the inner receiving portion 3a in a circumferential direction (direction of arrow B). At this time, as shown in FIG. 6, a lower edge 7b of the flexible flat cable 7, disposed parallel to a plane perpendicular to the center axis of the volute of the flexible flat cable 7, slides on an annular bottom surface 3b of the inner receiving portion 3a, and also this lower edge 7b of the flexible flat cable 7 slides on a flange surface 5a formed on the outer periphery of the rotator 5. An effect at the annular bottom surface 3b of the inner receiving portion 3a will be explained for example. As shown in FIG. 7, the annular bottom surface 3b of the related construction is disposed parallel to a plane perpendicular to the center axis of the volute of the flexible flat cable 7, and therefore the flat cable 7 slides on the annular bottom surface 3b over the entire range of this annular bottom surface 3b, as shown in FIG. 8. As a result a harsh sliding sound is produced. The same is the case with the lower edge 7b of the flexible flat cable 7 and the flange surface 5a of the rotator 5.
The surface roughness of each of the annular bottom surface 3b and the flange surface 5a is increased in order to suppress the production of the sliding sound as much as possible. However, with the lapse of time, the surface roughness of each of the annular bottom surface and the flange surface becomes lowered, so that a sliding sound is produced. Therefore, although the production cost of molds is increased in order to enhance the surface roughness, sufficient effects can not be obtained.
And besides, the maintenance cost for the molds increased in order to maintain the required surface roughness.
This invention has been made under the above circumstances, and an object of the invention is to provide a rotary connector in which the production of a sliding sound can be reduced without increasing the surface roughness, thereby achieving a reduced production cost and an enhanced quality at the same time.
To achieve the above object, according to a first aspect of the invention, there is provided a rotary connector comprising:
a cylindrical fixed member defining an inner receiving portion;
a rotary member rotatably concentrically mounted in the inner receiving portion defining an annular space in cooperation with the cylindrical fixed member;
a spirally-wound flexible flat cable received in the annular space, wherein an outer periphery-side end of the flexible flat cable is fixed to the fixed member and a center-side end of the flexible flat cable is fixed to the rotary member; and
a contact surface defining the annular space in cooperation with the cylindrical fixed member and the rotary member, wherein a portion of the contact surface adjacent to at least one of the cylindrical fixed member and the rotary member has a slanting surface slanting downwardly so that the flexible flat cable separates from a middle portion of the contact surface.
According to a second aspect of the invention, in the rotary connector of the first aspect, the contact surface comprises a flange surface integrally formed with the rotary member and an annular bottom surface integrally formed with the cylindrical fixed member.
According to a third aspect of the invention, in the rotary connector of the second aspect, the slanting surface is formed on at least one of the flange surface and the annular bottom surface.
In this rotary connector, the annular bottom surface of the inner receiving portion, with which the lower edge of the flat flexible cable, disposed parallel to the plane perpendicular to the center axis of the volute of the spirally-wound flat cable, is held in sliding contact, is formed by the slanting surface slanting downwardly radially inwardly, and the range of sliding contact between the lower edge of the flexible flat cable and the annular bottom surface is reduced. As a result, a sliding sound, produced as a result of sliding movement of the flexible flat cable on the annular bottom surface, is reduced. And besides, it is not necessary to increase the surface roughness of the annular bottom surface in order to reduce the sliding sound, and therefore the production cost of molds is reduced.
In this rotary connector, the flange surface (formed on the outer periphery of the rotary member), with which the lower edge of the flexible flat cable, disposed parallel to the plane perpendicular to the center axis of the volute of the spirally-wound flexible flat cable, is held in sliding contact, is formed by the slanting surface slanting downwardly radially outwardly, and the range of sliding contact between the lower edge of the flexible flat cable and the flange surface is reduced. As a result, a sliding sound, produced as a result of sliding movement of the flexible flat cable on the flange surface, is reduced. And besides, it is not necessary to increase the surface roughness of the flange surface in order to reduce the sliding sound, and therefore the production cost of molds is reduced. In the invention, the annular bottom surface is formed by the slanting surface, and in addition the flange surface is formed by the slanting surface, and in this case the lower edge of the flexible flat cable slides on the two regions, that is, the annular bottom surface and the flange surface, in a line-contact condition, so that the effect of reducing the sliding sound is made maximum.